Efi Injector Size Calculator

EFI Injector Size Equation:

\[ Injector\ Size\ (lb/hr) = \frac{HP \times BSFC}{Number\ of\ Injectors \times Duty\ Cycle} \]

Horsepower (HP):

Brake Specific Fuel Consumption (BSFC):

lb/HP-hr

Number of Injectors:

count

Duty Cycle:

fraction (0-1)

Injector Size Required:

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1. What is EFI Injector Size Calculation?

The EFI injector size calculation determines the required fuel injector flow rate (in pounds per hour) based on engine horsepower, brake specific fuel consumption, number of injectors, and their duty cycle. Proper injector sizing is critical for engine performance and reliability.

2. How Does the Calculator Work?

The calculator uses the injector size equation:

\[ Injector\ Size\ (lb/hr) = \frac{HP \times BSFC}{Number\ of\ Injectors \times Duty\ Cycle} \]

Where:

\( HP \) — Engine horsepower
\( BSFC \) — Brake specific fuel consumption (typically 0.45-0.65 lb/HP-hr for gasoline engines)
\( Number\ of\ Injectors \) — How many fuel injectors the engine has
\( Duty\ Cycle \) — Maximum injector duty cycle (typically 80% or 0.8 for safety margin)

Explanation: The equation calculates the fuel flow required per injector to support the engine's power output at the specified duty cycle.

3. Importance of Proper Injector Sizing

Details: Correct injector sizing ensures adequate fuel delivery without running injectors at 100% duty cycle, which can cause poor fuel atomization, inconsistent delivery, and injector failure.

4. Using the Calculator

Tips: Enter realistic values for all parameters. For BSFC, use 0.45-0.50 for efficient modern engines, 0.55-0.65 for older or high-performance engines. Duty cycle should typically be 0.8 (80%) for safety margin.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical BSFC value for gasoline engines?
A: Naturally aspirated engines: 0.45-0.50, Turbocharged engines: 0.55-0.65, High-performance race engines: up to 0.70.

Q2: Why not run injectors at 100% duty cycle?
A: Running at 100% leaves no safety margin, causes inconsistent fueling, and can lead to injector failure from overheating.

Q3: How do I convert lb/hr to cc/min?
A: Multiply lb/hr by 10.5 (approximately) to get cc/min.

Q4: What if I have different sized injectors?
A: This calculator assumes all injectors are the same size. For staged injection or different sizes, more complex calculations are needed.

Q5: How does fuel pressure affect injector flow?
A: Flow rate changes with the square root of pressure ratio. Double pressure = ~1.41x flow (assuming same injector).